st: roblpr update

The roblpr routine (Robinson log-periodogram regression estimator) of
Baum and Wiggins, originally published in STB-57, has been updated to
Stata 8.2. The new version may be applied to a single timeseries of a
panel or to all series of a panel using the by prefix.
The revised routine is available from SSC or, if already installed,
via adoupdate.